Which Fuel Properties for Improved CAI Combustion? Study of Fuel Impacts on the Operating Range of a CAI PFI Engine

摘要

This paper presents the major results of an International Consortium study carried out by IFP and focused on the evaluation of fuel impacts on Controlled Auto Ignition (CAI) combustion. The formulation and tests of two adapted fuel matrix have allowed identifying and evaluating the main fuel properties that can improve CAI combustion for a maximum enlargement of the CAI operating range. CAI combustion mode appears as one promising solution for the development of low CO_2 gasoline engines. Fuel properties can then be key parameters to improve the performances of CAI engines. During a first step of the study, steady state tests have been performed on a single cylinder Port Fuel Injection Spark Ignition (PFI SI) engine, with real fuels. Through the set up of dedicated test methodologies and the development of innovative solutions for fuel impacts analysis, four major fuel properties have been highlighted as potential CAI combustion improvers: Research Octane Number (RON), Latent Heat of Vaporization (LHV), Formaldehyde Formation Potential (FFP) and EGR sensitivity. FFP and EGR sensitivity have been defined and evaluated in this study. They are deeply linked to the fuel chemical composition. Thus, these fuel properties help to understand the competition between thermal and chemical phenomenon in the set up of CAI combustion. Based on these parameters, optimized fuel formulations have allowed a significant enlargement of the CAI operating range, especially in the low engine speed / low load region. Moreover, this work has led to a general improvement of the understanding of CAI combustion process and allowed a deep exploration of the possible fuel role for improved CAI combustion in gasoline engines. These findings have been applied and more deeply studied in the rest of the consortium study, on a GDI engine.